We address the following question: Is there a difference (D) between the amount of time for auditory and visual stimuli to be perceived? On each of 1000 trials, observers were presented with a light-sound pair, separated by a stimulus onset asynchrony (SOA) between -250 ms (sound first) and +250 ms. Observers indicated if the light-sound pair came on simultaneously by pressing one of two (yes or no) keys. The SOA most likely to yield affirmative responses was defined as the point of subjective simultaneity (PSS). PSS values were between -21 ms (i.e. sound 21 ms before light) and +150 ms. Evidence is presented that each PSS is observer specific. In a second experiment, each observer was tested using two observer-stimulus distances. The resultant PSS values are highly correlated (r = 0.954, p = 0.003), suggesting that each observer's PSS is stable. PSS values were significantly affected by observer-stimulus distance, suggesting that observers do not take account of changes in distance on the resultant difference in arrival times of light and sound. The difference RTd in simple reaction time to single visual and auditory stimuli was also estimated; no evidence that RTd is observer specific or stable was found. The implications of these findings for the perception of multisensory stimuli are discussed.
An apparently clear case of category-specific naming impairment selectively affecting animals was detected in a patient who had recovered from herpes simplex encephalitis. However, subsequent investigation demonstrated that these category-specific effects could be eliminated by controlling simultaneously for three factors in picture naming: word frequency, concept familiarity, and visual complexity. The results emphasize the importance of controlling for all factors pertinent to picture naming when attempting to demonstrate category specificity in picture naming. Further testing indicated that deficits were also apparent when naming to definition was required, and some impairment in the ability to answer questions about objects and living things was also noted. Theoretical implications of these data are considered.
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